Interestingly I’m working on converting Ubersreik Adventures 1 & 2 and the starter set to 5e to teach my partner, my brother and his wife to play 5e. I’ve only really started on maps and tokens but about to start working on NPCs. I need to get my head around reduced encounter number days. That seems to be the toughest stumbling block for now.I'm currently running the Horned Rat. I am not trying to poo on this idea, but WFRP is so simple a system why not just use that. I think you are going to really really over complicate things using 5e. WFRP and Empire in Ruins is a perfect match.
If you want to play 5e for this have at it, but the Enemy WIthin "remaster" is just so smooth. I am having a blast running this, and I think if I was to do this in 5e I'd really be having problems.
I love complexity and though WFRP is simple, it really covers its bases for the "3 pillars" extremely well, and that exploration and investigation abilities are going to be really important for this campaign. WFRP makes it that any character can really contribute to the investigation. I think you have to re-engineer 5e a bit to make some classes contribute well.
As for WFRP 4e, we’re about 6 sessions into Enemy Within and I’ve dropped in The Oldenhaller Contract. I wouldn’t say it is simple, but I’m finding it very enjoyable.